The present invention relates to a four-stroke engine. DE 42 27 433 C2 discloses a four-stroke engine for portable implements and has a diaphragm carburetor, whereby for the drive of a fuel pump of the carburetor, the pressure pulsations in the intake pipe between the carburetor and the cylinder are utilized. For this purpose, a pressure chamber of the intake channel communicates via a pulse line with the drive chamber of the pump. During operation of such four-stroke engines, it has been shown that the pressure fluctuations in the intake pipe are not always sufficient for driving the fuel pump. In particular during acceleration, during rapid opening of the butterfly valve of the diaphragm-type carburetor, a break in pressure occurs that limits the fuel supply.
It is therefore an object of the present invention to ensure a reliable supply of fuel in all operating situations for such a four-stroke engine.